We will investigate if the reduced incorporation of norepinephrine into portal-mesenteric veins and an increased uptake into both atria and mesenteric artery of adult spontaneoulsy hypertensive rat also occur in their prehypertensive age. We will also investigate whether reduced uptake of exogeneous norepinephrine is associated with a defect in the neuronal membrane transport system and/or storage vesicle binding, or high degradative enzyme activity. Electron and light microscopic studies of the vascular blood vessels from different age groups of spontaneously hypertensive rate will be compared.